Among the various kinds of bioalcohol, for example, bioethanol is manufactured mainly by degrading and refining the sugar of, for example, corn or wheat. Nowadays, bioethanol is widely used in the world as an alternate fuel to petroleum (gasoline) or as a fuel to be mixed with gasoline, and the amount of bioethanol used tends to increase year by year. For example, in a process of storing and transporting bioethanol or in a process of mixing bioethanol with gasoline, a steel material is used. However, since bioethanol is highly corrosive to steel material, that is, since an SCC tends to be generated in a portion of a steel material in which there is a high residual stress or which is exposed to a fluctuating load, it is difficult to handle bioethanol.
The fact that an extremely small amount of carboxylic acid such as acetic acid exists as an impurity in a process of manufacturing bioethanol and the fact that bioethanol absorbs water, dissolved oxygen, and chloride ions in storage contribute to an increase in the corrosiveness of bioethanol. Therefore, there is a demand for an SCC test method for correctly evaluating the SCC susceptibility of a steel material in a bioalcohol environment.
For example, Non Patent Literature 1 and Non Patent Literature 2 give reports regarding a method for evaluating SCC susceptibility on the basis of the state of a fracture surface, after fracturing, which has been generated by applying strain to a tensile test piece at a constant strain rate of 2×10−6 in/s to 8×10−7 in/s.
In addition, for example, Non Patent Literature 3 gives a report regarding a method for evaluating SCC susceptibility on the basis of a crack growth distance in a test in which a fluctuating load corresponding to 60% to 80% of the tensile strength of a steel material at a frequency of 1.4×104 Hz is applied to a tensile fatigue test piece provided with a precrack in a simulated bioethanol solution.